A method of fabricating a solar cell for solar light power generation is as follows. First, after preparing a substrate, a back electrode layer is formed on the substrate, and patterned by a laser to form a plurality of back electrodes.
Thereafter, a light absorbing layer, a buffer layer, and a high resistance buffer layer are sequentially formed on the back electrodes. A scheme of forming a Cu(In,Ga)Se2 (CIGS) based-light absorbing layer by simultaneously or separately evaporating copper (Cu), indium (In), gallium (Ga), and selenium (Se) and a scheme of performing a selenization process after a metallic precursor film has been formed, have been extensively used in order to form the light absorbing layer. The energy bandgap of the light absorbing layer is in the range of about 1 eV to 1.8 eV.
Then, the buffer layer including cadmium sulfide (CdS) is formed on the light absorbing layer through a sputtering process. The energy bandgap of the buffer layer may be in the range of about 2.2 eV to 2.4 eV. After that, the high resistance buffer layer including zinc oxide (ZnO) is formed on the buffer layer through the sputtering process. The energy bandgap of the high resistance buffer layer is in the range of about 3.1 eV to about 3.3 eV.
Thereafter, holes patterns may be formed in the light absorbing layer, the buffer layer, and the high resistance buffer layer.
Then, a transparent conductive material is laminated on the high resistance buffer layer, and the hole patterns are filled with the transparent conductive material. Accordingly, a transparent electrode layer is formed on the high resistance buffer layer, and connection wires are formed inside the holes patterns. A material constituting the transparent electrode layer and the connection wires may include aluminum doped zinc oxide (AZO). The energy bandgap of the transparent electrode layer may be in the range of about 3.1 eV to 3.3 eV.
Then, the hole pattern is formed in the transparent electrode layer, so that a plurality of solar cells may be formed. The transparent electrodes and the high resistance buffers correspond to the cells, respectively. The transparent electrodes and the high resistance buffers may be provided in the form of a stripe or a matrix.
The transparent electrodes and the back electrodes are misaligned from each other and electrically connected with each other by the connection wires. Accordingly, the solar cells may be electrically connected to each other in series.
As described above, in order to convert the solar light into electrical energy, various solar cell apparatuses have been fabricated and used. One of the solar cell apparatuses is disclosed in Korean Unexamined Patent Publication No. 10-2008-0088744.
Meanwhile, according to the related art, when cadmium sulfide (CdS) is employed, the problem related to cadmium (Cd) occurs. Accordingly, in order to form a buffer layer without Cd, zinc sulfide (ZnS) may be used for the buffer layer. When ZnS is employed, a front electrode layer is directly deposited on the ZnS buffer layer without forming a high resistance buffer layer on the ZnS buffer layer.
However, since the ZnS buffer layer has resistance higher than that of the CdS buffer layer, the thickness of the ZnS buffer layer is restricted. Accordingly, when the front electrode layer is deposited on the ZnS buffer layer, damage may be caused to the upper portion of the buffer layer and/or the light absorbing layer.
Accordingly, the necessities for the fabrication of a buffer layer, which can solve the above problem when a ZnS buffer layer is used, and a solar cell including the buffer layer are raised.